The present invention relates to position sensing devices and, more particularly, to a scanning device comprising a position sensing device having a movable photosensing element.
Hand-held scanning devices are portable imaging devices that generate machine-readable image data (sometimes referred to herein simply as image data) representing an image of an object. Generating image data representative of an object is sometimes referred to as xe2x80x9cimagingxe2x80x9d or xe2x80x9cscanningxe2x80x9d the object. Some scanning devices generate image data representing a narrow xe2x80x9cscan linexe2x80x9d portion of the object being imaged. During the Ad imaging process, the scanning device is moved relative to the object being imaged. As the scanning device is moved relative to the object, the scanning device generates image data representing a plurality of sequential scan line portions of the image of the object. The image of the object is, accordingly, represented by the image data of the cumulation of sequential scan lines similar to the image of the object represented by a conventional video display.
The image of the scan line portion of the object is focused onto a linear array of photodetector elements (sometimes referred to herein simply as photodetectors). The photodetectors may, as an example, be mounted to a plurality of linearly arranged electronic segments such as contact image sensors as are known in the art. The photodetectors may also be etched into a single semiconductor as is common in a charge-coupled device. The individual photodetectors generate image data representing discrete portions of the image of the scan line portion of the object. The image data may, as an example, be represented by a series of voltages, wherein a relatively high voltage represents a relatively high intensity of light received by a photodetector and a relatively low voltage represents a relatively low light intensity received by a photodetector.
The image data generated by the photodetectors is transmitted to a processor. One of the functions of the a processor is to create a data base or similar electronic structure that indicates the positions of the scan lines relative to the positions on the object from where the scan lines were generated. Alternatively, the data base may indicate the locations of the scan lines relative to each other. The data stored in the data base and the image data are used by the processor to replicate the image of the object. As an example, in the situation in where the scanning device is generating image data representing a two-dimensional object, such as text located on a sheet of paper, the hand-held scanning device may be moved in any direction on the paper. Accordingly, the scan line portions may be generated from virtually any location on the paper, which leads to the image data representing the image of the object consisting of a plurality of scan line portions that may be skewed over the surface of the paper. In order to accurately replicate the image of the object, the hand held scanning device uses the data stored in the data base to determine the proper placement of the scan line portions of the image of the paper. The processor may then create an electronic image of text printed on the paper by known processing techniques, e.g., stitching software.
Examples of hand-held scanning devices are described in the following United States patents and patent applications, which are all hereby incorporated by reference for all that is disclosed therein: U.S. Pat. No. 5,552,597 of McConica for HAND-HELD SCANNER HAVING ADJUSTABLE LIGHT PATH; U.S. Pat. No. 5,646,394 of Steinle for IMAGING DEVICE WITH BEAM STEERING CAPABILITY; U.S. Pat. No. 5,646,402 of Khovaylo et al. for EXPANDABLE HAND-HELD SCANNING DEVICE; U.S. Pat. No. 5,723,859 of Kerschner et al. for LINE CONTACT HAND-HELD SCANNING DEVICE AND METHOD HAVING A LIGHT PATH SUBSTANTIALLY PERPENDICULAR TO THE ORIENTATION OF THE OBJECT AT A LINE PORTION; Ser. No. 09/120,641 of Sims et al. for HAND HELD SCANNING DEVICE filed on Jul. 29, 1998; and Ser. No. 09/120,637 of Sims et al. for HAND HELD SCANNING DEVICE filed on Jul. 30, 1998.
A problem replicating the image of the object may be encountered if the velocity or position of the scanning device relative to the object becomes unknown during the scanning process. For example, if the scanning device is imaging one thousand scan line portions of the image of the object per second and the scanning device is moving along a single axis at a constant rate of one inch per second relative to the object, each scan line represents one one-thousandth of an inch of the image of the object. If the correct velocity of the scanning device relative to the object has been conveyed to the processor, the processor will create a data base indicating that each scan line represents one one-thousandth of and inch of the image of the object. Alternatively, the processor will indicate that each scan line is located one one-thousandth of an inch from an adjacent scan line. Based on the image data and the data stored in the data base, the processor may accurately replicate the image of the object. If, however, the velocity of the scanning device relative to the object is decreased and the decreased velocity is not conveyed to the processor, the processor will continue to process the image data as though each scan line represents one one-thousandth of an inch of the object. Each scan line, however, will represent less than one one-thousandth of an inch of the object. Accordingly, the image of the object will be compressed. If, on the other hand, the velocity of the scanning device relative to the object is increased and the increased velocity is not conveyed to the processor, the image of the object will be expanded.
Accurately replicating an image of an object when either the velocity or position of the scanning device relative to the object becomes unknown is impossible. If the position or velocity is not known, the processor will not know where the scanning device is located relative to in the object as the scan lines are being generated. Accordingly, the processor will not be able to properly place the scan line portions relative to each other so as to accurately replicate the image of the object. This problem is exacerbated in hand-held scanning devices where the scan lines may be generated from anywhere on the object and are often skewed over the surface of the object.
In order to overcome these problems, scanning devices use position sensors to detect the position of the scanning device relative to the object. The position sensors output position information pertaining to the position of the scanning device relative to the object as the scan line portions of the image of the object are being generated. This position information is conveyed to the processor where it is incorporated into the above-described data base.
In some scanning devices, the position sensor takes the form of an optical sensor which may be rigidly affixed to the scanning device. The optical sensor is used to determine the position of the scanning device relative to the object being scanned. The optical sensor is a two-dimensional array of photodetectors that periodically generates image data from a small two-dimensional area portion of the object being scanned. A processor receives this image data and identifies distinct features in the area portion of the object. In the example where the object is text printed on a sheet of paper, the distinct features may be inherent irregularities in the surface of the paper. The irregularities may, for example, be caused by pulp material used to manufacture the paper.
The positions of these distinct features relative to the optical sensor are stored in a memory device. As the scanning device is moved relative to the object, the positions of these distinct features move relative to the optical sensor. The processor compares the new positions of these distinct features to the positions stored in the memory device. Based on these comparisons, the processor is able to determine the position, direction of movement, and velocity of the optical sensor, and thus, the scanning device, relative to the object. Accordingly, the processor is able to create the above-described data base because the locations of the scan line portions of the image of the object relative to each other may be readily determined.
Some scanning devices have several of these two-dimensional optical sensors rigidly affixed at various positions relative to the linear array of photodetectors. For example, the scanning device may have two optical sensors spaced a distance from each other. The scanning device is able to compare the movement data from each optical sensor to determine the amount of movement, including rotational motion, the scanning device has undergone. As the distance between the optical sensors increases, the accuracy to which the scanning device is able to determine rotational motion increases accordingly.
These optical sensors, however, tend to be some of the more expensive components comprising the scanning device. Two of the factors that influence the cost of an optical sensor are its area and its concentration of photodetectors. The cost of an optical sensor having a larger area or higher concentration of photodetectors is substantially more than an optical sensor having a smaller area or a lesser concentration of photodetectors. The sensitivity of the optical sensor, however, is proportional to its area and its concentration of photodetectors. An optical sensor with a large area and a high concentration of photodetectors is able to determine position with much greater accuracy than an optical sensor with a small area and a low concentration of photodetectors. Accordingly, in order to accurately determine the position of a hand-held scanning device, optical sensors having large areas and high concentrations of photodetectors are preferred. These optical sensors, however, substantially increase the cost of the hand-held scanning device.
Therefore, a need exists for a hand-held scanning device that is able to accurately determine its position without a substantial increase of the cost of the scanning device.
A position sensing device for determining the position of an object relative to a surface is disclosed herein. The position sensing device may comprise a substrate associated with the object; an actuator having a first portion and a second portion wherein the first portion is attached to the substrate and wherein the second portion is movably mounted to the first portion; and a two-dimensional photosensor array attached to the actuator second portion. A light path may extend between a plane and the two-dimensional photosensor array and a lens may be positioned in the light path. A processor may be electrically connected to the actuator and the two-dimensional photosensor array.
The two-dimensional photosensor array may have a two-dimensional array of photodetectors mounted to a surface. The photodetectors generate machine-readable image data representative of an image focused onto the photodetectors. The two-dimensional photosensor array is generally smaller than those used in conventional scanning devices. The concentration of photodetectors on the surface may, however, be substantially equivalent to the concentration of photodetectors used in conventional scanning devices.
The two-dimensional photosensor array generates image data representative of a two-dimensional area portion of the surface as the object is moved relative to the surface. The processor receives the image data and identifies the locations of distinct features in the image of the area portion. of the surface relative to the two-dimensional photosensor array. As the object moves relative to the surface, the images of the distinct features move relative to the two-dimensional photosensor array. During this period, the processor instructs the actuator to move the two-dimensional photosensor array to track the distinct features. By determining the movement of the images of the distinct features relative to the two-dimensional photosensor array and the amount of movement the actuator moves the two-dimensional photosensor array, the processor calculates the displacement of the object relative to the surface. The processor may then determine the velocity and position of the object relative to the surface.